1. Field of the Invention
This invention relates to devices for the attachment of an orthodontic appliance to a tooth and methods for making such a device.
2. Description of the Prior Art
The well-known practice of using bands to secure orthodontic appliances to the teeth is not generally desirable because bands create spaces between the teeth which must be closed at the conclusion of the orthodontic treatment. A bracket made of plastic and bonded directly to the tooth has been utilized for attachment of an orthodontic appliance directly to the tooth, thereby eliminating the band, as is shown in U.S. Pat. No. 3,303,565. Even though a plastic bracket bonds well to a tooth, such brackets have not generally provided the structural strength and control required for many types of orthodontic treatment. Thus, metal brackets fixed to composite metal and flexible plastic bases have been used in attempting to provide greater rigidity, as shown, for example, in U.S. Pat. No. 3,250,003.
A series of openings through a base pad, either metal, U.S. Pat. No. 3,932,940, or plastic, U.S. Pat. No. 3,765,091, on to which an orthodontic appliance is mounted, have been utilized with a suitable cement to help retain and bond the pad to the tooth. The holes allow the cement to flow into the openings to provide additional mechanical strength to the bond between the pad and the tooth. However, such plastic bases suffer from a lack of rigidity although providing good bonding, while such metal bases suffer from weak bonding while providing good rigidity. In both instances, the cement flows through the holes into the orthodontic appliance when being bonded to the tooth. The cement can not be immediately removed, because attempting to do so would move the device while the cement is curing, thereby negating the precise positioning required for orthodontic treatment. However, if the orthodontist waits to remove the excess cement from the appliance until the pad is reasonably securely bonded to the tooth, the cement has already bonded itself to the appliance, and therefore is difficult to remove.
Another base of this type is a pad of metal screen or mesh, to which the orthodontic appliance is attached by spot welding. Such devices, currently sold by American Orthodontics, Sheboygan, Wis., suffer from a weak attachment of the appliance to the pad, as well as not providing the strength of bonding of a plastic base or the rigidity of a metal base, and permitting an even greater amount of cement to pass through the base pad and contact the appliance. In a modified type of such a device, also sold by American Orthodontics, the appliance is mounted on a metallic base pad, which may be either plain or perforated, to which a pad of metal screen or mesh is attached by spot welding, so as to fix the screen to the base pad on the side of the pad opposite the appliance. Such a device, if not perforated, avoids the problem of excess cement flowing into the appliance by shielding the appliance from the cement, which must flow outwardly from the periphery of the pad, not through it. However, the spot welds destroy the mesh structure at the points of attachment of the screen to the pad, thereby decreasing the effectiveness of the adhesive in bonding the mesh to the tooth. Because of the flexible nature of the screen, many spot welds are necessary to ensure rigidity of this type composite pad, so that the mesh is not very effective. Alternatively, if only a few spot welds are utilized, the mesh flexes so that the effectiveness of the appliance in the orthodontic treatment diminishes.